We have measured HIV-1 recombination rates at several distances and demonstrated that recombination is a very powerful tool for reassorting the HIV-1 genome. We have identified a major restriction to intersubtype HIV-1 recombination, and are currently studying other restrictions to and facilitators of HIV recombination and replication. We have also demonstrated that other lentiviruses such as HIV-1 and SIVagm can also recombine at high frequencies, indicating that high frequency of recombination is a common feature in primate lentivirus replication. We have extended these studies to examine whether distinct lentiviruses can recombine with one another. In addition to studying the frequency and limitation of recombination, it is also important to understand the consequences of recombination. To address this aspect of recombination, we are currently examining the properties of recombinant viruses, and whether certain recombinants have a selective advantage in a given environment. Because it is thought that zoonotic events generated both HIV-1 and HIV-2, we have also constructed hybrid viruses to study whether recombination can facilitate the adaptation to new hosts.